TiddlyWiki is an open-source single page application wiki in the form of a single HTML file that includes CSS, JavaScript, and the content.

Mattermost is an open source, private cloud Slack-alternative, Workplace messaging for web, PCs and phones. MIT-licensed.

WriteMonkey is a full-screen writing environment that lets you focus on what you're trying to say, and forget the rest.

TagSpaces is an open source data manager and file navigator. It helps organize files on local drives by adding tags to files.